An innovative altimetry processing method that generates improved ice sheet elevation data from Copernicus Sentinel-3 observations has been developed by scientists at CLS (Collecte Localisation Satellites).
The project is supported by ESA as part of its long-standing commitment to enabling advances in polar altimetry, which includes facilitating cutting-edge cryosphere science, providing operational land and sea ice data products, and preparing future missions such as CRISTAL.
The new technique – presented in the EGUsphere pre-print repository – is expected to improve understanding of the surface elevation change in the polar ice sheets. This is crucial for investigating the broader impacts of climate change, including ice dynamics, ocean circulation, and environmental shifts that drive sea level rise and other global changes.
Sentinel-3 of the European Union’s Copernicus Earth Observation Programme carries the dual-frequency Synthetic Aperture Radar altimeter (SRAL), which monitors surface elevation by emitting a radar pulse and measuring the time it takes to bounce back to a receiver.
Copernicus Sentinel-3 over ocean and ice
Copyright:ESA
However, certain surface characteristics, such as the presence of a steep slope, are known to limit the accuracy of elevation data retrieved using conventional altimetry techniques.
To address this challenge, CLS developed and refined an innovative data processing chain, named the Altimeter data Modelling and Processor for Land Ice (AMPLI). The project was supported and funded by the French space agency (CNES) and ESA.
AMPLI combines Sentinel-3 observations, processed using the unfocused Synthetic Aperture Radar technique, with a high-resolution digital elevation model (DEM) called the Reference Elevation Model of Antarctica (REMA), which provides an accurate static 3D representation of Antarctica’s terrain.
A new innovative altimetry data processing method to reveal the potential of Sentinel-3 for ice sheet monitoring
Copyright:Contains modified Copernicus Sentinel data (2019-2022)/processed by CLS
The processing chain uses both data sources to model the exact point at which each radar pulse impacts the surface of the ice sheet, so that precise elevation measurements can be derived along the satellite tracks.
To assess the performance of the AMPLI processing method, its outputs were compared against an ice elevation product from ICESat-2, an advanced laser altimetry mission from NASA.
The research team reported that AMPLI topography estimates aligned closely with co-located ICESat-2 estimates, with an agreement at the decimetre-level between the two missions on average over the Antarctic ice sheet.
Furthermore, the assessments demonstrated a substantial improvement compared to conventional Sentinel-3 products. The accuracy of the estimated topography was significantly more uniform across Antarctica, and the measurement precision was improved by a factor of about 10 over the periphery of the ice sheets, where terrain slope is greater than 0.5 degrees.
While a DEM represents a static view of surface terrain, radar altimetry can observe topographical changes over time, thanks to the periodic revisit of the satellite. This benefit was explored in the study’s final step, in which the team evaluated the performance of AMPLI in tracking temporal changes to ice sheet elevation, which is crucial for long-term climate studies.
Surface elevation change maps, covering from 2019 to 2022, produced by Sentinel-3 AMPLI and ICESat-2 were shown to align strongly, demonstrating that AMPLI can be used to reliably measure how ice sheet elevation evolves over long time periods
Jerome Bouffard, ESA’s Mission Manager for Copernicus Sentinel-3, says, “As ESA advances its polar observation capabilities, this breakthrough in land ice data processing is a key step toward more accurate monitoring of ice sheet dynamics. By leveraging multi-mission datasets including Copernicus Sentinel-3 and the upcoming CRISTAL mission, scientists can better assess long-term cryosphere changes and gain crucial insights into climate change impacts.”
Jérémie Aublanc, research engineer and altimetry expert at CLS, says, “Satellite radar altimetry was initiated several decades ago to monitor the oceans. Over time, instruments have improved, and together with the development of dedicated data processing algorithms, this has enabled precise topographic measurements of other surfaces. Our innovative processing method has yielded unprecedented results over the Antarctic ice sheet, exceeding our expectations. The findings are of major importance, as they unveil the potential of Sentinel-3 mission for polar ice sheet monitoring.”
AMPLI data coming soon to the data space ecosystem
In parallel to the preparation of the manuscript describing method and results, a complete reprocessing of the Sentinel-3 mission with the AMPLI software was completed at the end of 2024. This was made possible thanks to the computational cluster at the Centre National d’Études Spatiales (CNES). The AMPLI reprocessing data set spans from 2016 to 2024, covering the Antarctic and Greenland ice sheets. These data, along with a dedicated user handbook, will be made freely available to users via the Copernicus Data Space Ecosystem in the coming months.
Preliminary results of Surface Elevation Change retrieved with Sentinel-3 AMPLI Products from the reprocessing data set, and covering 2019-2024 period (Sentinel-3A and Sentinel-3B combined)
Copyright:Contains modified Copernicus Sentinel data (2019-2022)/processed by CLS
About the Copernicus Sentinels
The Copernicus Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to the European Union's Copernicus environmental programme.
The European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites on behalf of the European Union and ensuring the flow of data for the Copernicus services, while the operations of the Copernicus Sentinels have been entrusted to ESA and EUMETSAT.
Did you know that?
Earth observation data from the Copernicus Sentinel satellites are fed into the Copernicus Services. First launched in 2012 with the Land Monitoring and Emergency Management services, these services provide free and open support, in six different thematic areas.
The Copernicus Land Monitoring Service (CLMS) provides geographical information on land cover and its changes, land use, vegetation state, water cycle and Earth's surface energy variables to a broad range of users in Europe and across the World, in the field of environmental terrestrial applications.
It supports applications in a variety of domains such as spatial and urban planning, forest management, water management, agriculture and food security, nature conservation and restoration, rural development, ecosystem accounting and mitigation/adaptation to climate change.
The Copernicus Climate Change Service (C3S) supports society by providing authoritative information about the past, present and future climate in Europe and the rest of the World.
References:
Aublanc, J., Boy, F., Borde, F., and Féménias, P.: A facet based numerical model to retrieve ice sheet topography from Sentinel-3 altimetry, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-1323, 2024.